diff --git a/cookbook/doctrine/reverse_engineering.rst b/cookbook/doctrine/reverse_engineering.rst
index efa393a0beb..39acef9da23 100644
--- a/cookbook/doctrine/reverse_engineering.rst
+++ b/cookbook/doctrine/reverse_engineering.rst
@@ -101,8 +101,9 @@ execute the second command only.
 
 .. tip::
 
-    If you want to use annotations, you can safely delete the XML (or YAML) files
-    after running these two commands.
+    If you want to use annotations, you must remove the XML (or YAML) files
+    after running these two commands. This is necessary as
+    :ref:`it is not possible to mix mapping configuration formats <book-doctrine-adding-mapping>`
 
 For example, the newly created ``BlogComment`` entity class looks as follow::